1. Field of the Invention
The invention relates to a control apparatus for a power transmission system including a dog clutch that connects or interrupts a power transmission path and that is actuated by a hydraulic actuator.
2. Description of Related Art
There is well known a power transmission system including a dog clutch that connects or interrupts a power transmission path and a hydraulic actuator that engages or releases the dog clutch. This is, for example, an automatic transmission described in Japanese Patent Application Publication No. 2003-74684 (JP 2003-74684 A). In the dog clutch, for example, after a synchronizer ring is synchronized with a synchronized gear, spline teeth provided on the inner periphery of a sleeve are meshed with spline teeth provided on the synchronizer ring and further meshed with spline teeth provided on the synchronized gear as a result of movement of the sleeve. Thus, the dog clutch is engaged. At the time of engaging such a dog clutch, there is a possibility that an uplock occurs because of the structure of a synchromesh mechanism. The uplock is such an engagement fault of the dog clutch (synchromesh mechanism) that the spline teeth cannot be meshed with each other because the tooth tips of the spline teeth contact each other and, as a result, the dog clutch is not engaged. In contrast, JP 2003-74684 A describes that, when an uplock of the dog clutch is detected in shifting into a speed position required through shift lever operation during engine stop, a shift is once carried out into a predetermined speed position different from the required speed position and then a shift into the required speed position is retried.
Incidentally, when hydraulic pressure for operating the hydraulic actuator is insufficient, there is a possibility that the sleeve cannot be moved to a completely engaged position of the dog clutch and, as a result, a shift into the required speed position cannot be carried out. Such a state where the sleeve cannot be moved is apparently the same as a state where there is an uplock. When an uplock is detected on the basis of the position of the sleeve and a synchronization state resulting from engagement, it is not possible to distinguish whether it is due to insufficient hydraulic pressure or it is due to occurrence of an actual uplock. Therefore, if it is uniformly determined that there is an uplock, and a retry operation (re-engagement operation of the hydraulic actuator) is carried out, it takes time to engage the dog clutch more than necessary, so there is a concern that drivability (for example, acceleration response) deteriorates. The above-described inconvenience is not publicly known.